The overarching goal of this project is to understand the mechanisms which underlie thyroid cancer development and progression such that successful therapies can be developed to treat advanced thyroid cancers that are refractory to current standard treatment modalities. For the current research proposal, the role of thioredoxin interacting protein (TXNIP) as a tumor suppressor and metabolic regulator in thyroid cancer development and progression will be defined. Rationale/Relation to Health: There are over 56,000 new cases of thyroid cancer diagnosed each year, and the incidence has been increasing over time. A subset of thyroid cancers is very aggressive and fails to respond to conventional treatments, and the unfortunate group of thyroid cancer patients that has anaplastic thyroid cancer (ATC) has a dismal prognosis with median survival of 3-5 months. There is a critical need to understand the mechanisms underlying the progression of thyroid cancer and development of ATC such that successful therapies can be developed. TXNIP functions to suppress tumor growth and progression in other cancer types though its role has never been investigated in thyroid cancer. The experiments here will define the role of TXNIP in the development and progression of thyroid cancer. These studies have the potential to identify novel therapeutic targets for patients with aggressive thyroid cancer. The hypothesis of the current proposal is that TXNIP is a tumor suppressor in thyroid cells and that TXNIP downregulation is important for tumor promotion and/or progression in thyroid cells. Specific Aims: In Aim 1, the role of TXNIP in the growth and malignant phenotype of thyroid cancer cells in vitro will be defined. In Aim 2, the role of TXNIP on the in vivo growth and malignant phenotype of thyroid cancer in an orthotopic thyroid cancer mouse model will be determined. Methods: Cell culture- and animal-based model systems will be utilized to define the role of TXNIP in thyroid cancer progression. In aggressive ATC cell lines shown to have low TXNIP expression, TXNIP will be overexpressed and effects on growth, metabolism, and other tumor-promoting capacities will be assessed. In less aggressive differentiated thyroid cancer (DTC) cells with high endogenous TXNIP expression, knockdown of TXNIP expression will be performed and the same phenotypic aspects as above will be assessed. Importantly, using the thyroid cancer cell lines with manipulated TXNIP expression, the role of TXNIP in tumor formation and progression will be directly tested in an established thyroid cancer mouse model. Expected results: It is expected that increasing the level of TXNIP in ATC cells will reverse the aggressive phenotype (i.e. diminish growth, invasion, metastasis, and overall survival of injected animals). Likewise, with decreasing the level of TXNIP expression in DTC cells, it is expected that development of a more aggressive phenotype will occur.